This invention relates to a test method and a test apparatus for use in a virtual path between a transmission side and a reception side in an asynchronous transfer mode (ATM) system.
In a conventional asynchronous transfer mode system of the type described, a virtual path is formed between a transmission side and a reception side before data transmission is carried out therebetween. In the asynchronous transfer mode, the virtual path should be tested in order to guarantee formation of the virtual path. For this purpose, an operation administration monitoring (OAM) cell is transmitted from the transmission side to the reception side through the virtual path after formation of the virtual path. Such an operation administration monitoring cell serves to make a continuity test, a characteristic test, a fault locating test, and the like.
More specifically, a predetermined pseudo noise (PN) pattern of a plurality of bits is inserted into the operation administration monitoring cell on the transmission side and is sent to the reception side to establish synchronization therein. The reception side receives the operation administration monitoring cell as a reception operation administration monitoring cell including a reception pseudo noise pattern which corresponds to the predetermined pseudo noise pattern and which might be different from the predetermined pseudo noise pattern due to jamming or the like on the virtual path. On the reception side, the reception pseudo noise pattern is compared with the predetermined pseudo noise pattern to produce an error bit number representative of the bit number of incoincidence between the reception and the predetermined pseudo noise patterns.
With this structure, a disorder of synchronization can be detected by monitoring the error bit number on the reception side. However, it is difficult to detect reception of a wrong cell to be destined to a wrong reception and a loss of a desired cell, while synchronization is established on the reception side.